Glow In The Dark Icing

Ok, so I was totally glued to the tv for a few weeks when Food Network's Last Cake Standing was on. I was totally entranced by something that the winner Mary Maher did on the cake she did as a team, the superhero cake. She used a glow in the dark icing. Does anyone know how to do this? She mentioned on the show somethng about the properties of quanine in Tonic Water...Any help greatly appreciated. I would love to use this technique on my boyfriend's upcoming 30th b-day on the 4th of July....thanx